Enhanced upper receiver is everything you need to convert your AR carbine or pistol to the exciting new 300 AAC Blackout (300 BLK) round. Features a nitrided, 1-7 twist barrel with M4 feed cuts, a Knight’s Armament URX free-floating handguard, and AAC'S 51T flash suppressor. 51T accepts the AAC 762-SDN-6 sound suppressor to make the gun nearly silent when used with subsonic ammunition. The nitride treated bore and chamber provide excellent corrosion resistance and a longer service life than standard chrome-lined barrels, and the full-profile M16 bolt/carrier group allows these uppers to function on a full-auto M16 lower as well as on semi-auto guns. Available with standard 16" Carbine barrel, designed to function with subsonic and supersonic ammunition. All barrels feature a 1-7 twist.